APC40 midi function / pangoscript

i tried to use new buttons for example "transition"
i wanna use one of the buttons below the main grid.

i had problems with the midi feedback.

I also tried with pangoscript, but dont find the correct function for transition and prompting it via IF-function.

so my wish is:
pushing the button on apc for transition => activates the function in beyond and the button at the apc gives an optical feedback (glows).
If i push the button again, the function gets inactive and the button stops glowing.